Adhesive Composition

ABSTRACT

An epoxy-based adhesive composition and methods for manufacturing the same are provided. The adhesive composition provides excellent adhesion strength, peel strength and impact-resistant strength uniformly over a wide temperature range.

TECHNICAL FIELD Cross-Reference to Related Applications

This application claims the benefit of priority based on Korean PatentApplication No. 10-2018-0086341 filed on Jul. 25, 2018, the disclosureof which is incorporated herein by reference in its entirety.

Technical Field

The present application relates to an adhesive composition.

BACKGROUND ART

Adhesives comprising epoxy resins, that is, epoxy resin-based adhesives,have high heat resistance and excellent adhesion strength and thus areused to bond or join various kinds of base materials. For example,recently, the epoxy resin-based adhesives have been used for metal-metaljoining or metal-plastic joining, and the like. In particular, when theepoxy resin-based adhesives are used in the automotive industry, thereis an advantage that the cost can be reduced and the weight of thevehicle body can be reduced by reducing the number of welds required formanufacturing vehicle body frames. As a result, there is a growingexpectation for application of epoxy resin adhesives in aerospace orwind power generation.

In consideration of accidents such as collisions, the epoxy resin-basedadhesives used for automobiles require not only excellent adhesionstrength but also impact-resistant strength. Then, these characteristicsshould be maintained uniformly over a wide range of temperatures inwhich automobiles are actually used, for example about −40 to 80° C.However, the epoxy resin-based adhesives according to the prior art havea problem that they do not provide sufficient strength for lowtemperature conditions such as −40° C.

DISCLOSURE Technical Problem

It is one object of the present application to provide an epoxyresin-based adhesive composition.

It is another object of the present application to provide an adhesivecomposition that provides excellent adhesion strength, impact strengthand shear strength over a wide temperature range.

The above objects and other objects of the present application can allbe solved by the present application described in detail below.

Technical Solution

In one example of the present application, the present applicationrelates to an adhesive composition comprising an epoxy-based resin. Theadhesive composition may be used to bond homogeneous or heterogeneousbase materials after curing. For example, the base material may comprisea metal component or a plastic component, whereby the adhesivecomposition may be used for metal-metal joining, metal-plastic joiningor plastic-plastic joining, and the like. A joining body (hereinafter,may be referred to as a composite or a structure) of such a basematerial can be used, for example, as a component of an automobile orthe like.

In the present application, the adhesive composition may comprise (a)one or more epoxy resins, (b) a modified epoxy resin having a polyetherstructure, (c) a core-shell rubber in the form of secondary particles inwhich two or more core-shell rubbers in the form of primary particlesare aggregated, and (d) one or more epoxy curing agents. The adhesivecomposition of the present application comprising all of theseconfigurations can provide excellent adhesion strength, impact-resistantstrength and shear strength uniformly for a structure formed using thecured product of the adhesive composition from a low temperature such as−40° C. to a high temperature such as 80° C.

(a) Epoxy Resin

When all the (a) to (d) configurations are included, the specificstructure of the epoxy resin used for the adhesive composition of thepresent application is not particularly limited. For example, the epoxyresin may be an epoxy resin having a saturated or unsaturated group, andmay be an epoxy resin containing a cyclic structure or an acyclicstructure. In addition, the specific kind of the epoxy resin used in thepresent application is not particularly limited either. For example, theepoxy resin may include a bisphenol-based epoxy resin such as bisphenolA series or bisphenol F series; a novolac-based epoxy resin; or anoxazolidone-containing epoxy resin, and the like.

In the present application, the epoxy resin (a) may be used togenerically mean an epoxy resin that does not have the properties of themodified epoxy resin (b) described below.

In one example, the epoxy resin may include a bisphenol A-based epoxyresin and/or a bisphenol F-based resin. For example, the trade nameYD-128, YDF-170 or YD-011 from Kukdo Chemical, and the like can be used.

In one example, the epoxy resin (a) may include a bisphenol A-basedepoxy resin and/or a bisphenol F-based resin, having an epoxy equivalentof less than 300. The epoxy equivalent of the epoxy resin used withinthe above range is not limited. For example, the epoxy equivalent of theepoxy resin may be 280 or less, 260 or less, 240 or less, 220 or less,or 200 or less. Although not particularly limited, the epoxy equivalentlower limit of the epoxy resin may be 100 or more, 110 or more, 120 ormore, 130 or more, 140 or more, or 150 or more.

In one example, the adhesive composition may comprise two or more epoxyresins that one or more features selected from an epoxy equivalent, amolecular weight or a viscosity are different from each other.

In one example, the adhesive composition may comprise two or more resinshaving different epoxy equivalents from each other. For example, withinthe epoxy equivalent range in the range of 120 to 700, two or more epoxyresins having different equivalents from each other may be used. Thatis, the adhesive may comprise an epoxy resin mixture (a) in which two ormore resins having different equivalents from each other are mixed.

In one example, the epoxy resin mixture (a) may comprise one or moreepoxy resins having an epoxy equivalent of 300 or more. For example, theepoxy equivalent of the epoxy resin may be 320 or more, 340 or more, 360or more, 380 or more, 400 or more, 420 or more, 440 or more, 460 ormore, 480 or more, 500 or more, 520 or more, 540 or more, 560 or more,580 or more, or 600 or more. Although not particularly limited, theepoxy equivalent upper limit of the resin may be 650 or less, 640 orless, 630 or less, or 620 or less.

In one example, the epoxy resin mixture (a) may comprise one or moreepoxy resins having an epoxy equivalent of 300 or more and one or moreepoxy resins having an epoxy equivalent of 300 or less.

In one example, the adhesive composition may comprise a bisphenol-basedA resin as an epoxy resin having an epoxy equivalent of less than 300.

In another example, the adhesive composition may further comprise abisphenol-based A resin as the epoxy resin having an epoxy equivalent of300 or more.

In one example, the adhesive composition may comprise a bisphenol-basedF-based resin as the epoxy resin having an epoxy equivalent of less than300.

In another example, the adhesive composition may further comprise abisphenol-based F-based resin as the epoxy resin having an epoxyequivalent of 300 or more.

In one example, the adhesive composition may comprise both of thebisphenol A-based resin and F-based resin satisfying the aboveequivalent.

When the epoxy equivalent increases, the crosslinking density maygenerally decrease while the viscosity increases, and the strengthobserved after the composition has cured may also be somewhat poor. Inaddition, when the epoxy equivalent decreases, there is a problem thatcannot fully expect the effect of using the epoxy-based adhesive.However, when the resins having a predetermined epoxy equivalent asabove are mixed and used, there is an advantage that can solve the aboveproblems.

In one example, the adhesive composition may comprise an epoxy resinhaving an epoxy equivalent of less than 300 in an amount of 15 parts byweight or more relative to the total content of the adhesivecomposition. Specifically, the adhesive composition may comprise anepoxy resin having an epoxy equivalent of less than 300 in an amount of20 parts by weight or more, 25 parts by weight or more, or 30 parts byweight or more. The content upper limit of the epoxy resin having anepoxy equivalent of less than 300 is not particularly limited, but maybe, for example, 55 parts by weight or less, 50 parts by weight or less,45 parts by weight or less, or 40 parts by weight or less.

In one example, the adhesive composition may comprise an epoxy resinhaving an epoxy equivalent of 300 or more in an amount of 1 part byweight or more relative to the total content of the adhesivecomposition. Specifically, the adhesive composition may comprise anepoxy resin having an epoxy equivalent of 300 or more in an amount of 2parts by weight or more, 3 parts by weight or more, 4 parts by weight ormore, or 5 parts by weight or more. The content upper limit of the epoxyresin having an epoxy equivalent of 300 or more is not particularlylimited, but may be, for example, 15 parts by weight or less, or 10parts by weight or less.

In one example, the epoxy resin or the epoxy resin mixture may be usedin an amount of 15 parts by weight or more, 20 parts by weight or more,25 parts by weight or more, 30 parts by weight or more, 35 parts byweight or more, 40 parts by weight or more, 45 parts by weight or more,50 parts by weight or more, or 55 parts by weight or more, relative tothe content of the total adhesive composition. The upper limit thereofis not particularly limited, but may be, for example, 80 parts by weightor less, 75 parts by weight or less, 70 parts by weight or less, or 65parts by weight or less.

In the present application, the adhesive composition may comprise a monoepoxy resin. In the present application, the mono epoxy resin may mean aresin having one epoxy functional group in the molecule. The mono epoxyresin is capable of lowering the viscosity of the adhesive, and isadvantageous in improving wettability, impact characteristics oradhesion (peeling) characteristics by adjusting the crosslinkingdensity. The mono epoxy resin may be referred to as a so-called diluent.

In one example, the mono epoxy resin may be used in an amount of 10parts by weight or less relative to the total content of the adhesivecomposition. Specifically, the content of the mono epoxy resin may be,for example, 9 parts by weight or less, 8 parts by weight or less, 7parts by weight or less, 6 parts by weight or less, or 5 parts by weightor less. The lower limit is not particularly limited, but may be, forexample, 0.5 parts by weight or more.

(b) Modified Epoxy Resin

The modified epoxy resin may be a polyether modified epoxy resin. Themodified epoxy resin may be a resin obtained by reacting anamine-terminated polymer, that is, an amine-terminated polyether withone or more epoxy resins, that is, a reactant thereof.

In one example, the amine-terminated polyether may be a polyalkyleneglycol such as polypropylene glycol, and the epoxy resin reacting withthis may be a bisphenol A-based epoxy resin or F-based epoxy resinsatisfying the equivalent.

In one example, the polyether modified epoxy resin may be a modifiedepoxy resin comprising an amine-terminated polyalkylene glycol unithaving an amine equivalent in a range of 300 to 2,000 and a unit of abisphenol A or bisphenol F epoxy resin having an epoxy equivalent in arange of 150 to 300. In the present application, the fact that the resincontains a predetermined unit may mean a state where in a resinstructure (main chain or side chain) formed by reacting one or morecompounds, the unit derived as the compounds are polymerized is includedtherein.

In one example, the amine equivalent of the amine-terminatedpolyalkylene glycol may be 400 or more, 500 or more, 600 or more, 700 ormore, 800 or more, or 900 or more, and may be 1,500 or less, 1,400 orless, 1,300 or less, or 1,200 or less.

In one example, in the polyether modified epoxy resin, the molar ratio(amine:epoxy) of the amine and the epoxy may be 1:4 or more. Morespecifically, the ratio may be 1:5 or more, 1:6 or more, 1:7 or more,1:8 or more, 1:9 or more, or 1:10 or more. The upper limit thereof isnot particularly limited, but may be, for example, 1:15. When the aboverange is satisfied, an excessive increase in molecular weight can besuppressed, and the effect of using the modified epoxy can be increased.

In one example, the polyalkylene glycol used to form the modified epoxyresin may have a weight average molecular weight in a range of 200 to1,500. The weight average molecular weight may be a polystyreneconversion molecular weight measured by GPC. When the above range issatisfied, it is possible to simultaneously increase adhesion strengthand impact strength of the adhesive while properly adjusting mechanicalstrength and shear strength.

The adhesive composition may comprise 30 parts by weight or less of thepolyether modified epoxy resin based on the content of the entireadhesive composition. For example, the content upper limit of themodified epoxy resin may be, for example, 29 parts by weight or less, 28parts by weight or less, 27 parts by weight or less, 26 parts by weightor less, or 25 parts by weight or less. Although not particularlylimited, the content lower limit of the polyether modified epoxy resinmay be, for example, 1 part by weight or more, 2 parts by weight ormore, 3 parts by weight or more, 4 parts by weight or more, 5 parts byweight or more, 6 parts by weight or more, 7 parts by weight or more, 8parts by weight or more, 9 parts by weight or more, or 10 parts byweight or more. When the use content of the modified epoxy resin is lessthan the above range, the effect of improving the impact strength is notsufficient, and when it exceeds the above range, the mechanical strengthand the shear strength of the adhesive are greatly lowered.

(c) Rubber

The adhesive composition comprises a core-shell rubber in the form ofsecondary particles in which two or more core-shell rubbers in the formof primary particles are aggregated.

In the present application, the “core-shell rubber” may mean aparticulate (solid) material having a rubber component in a core portionand having a structure in which a shell material is grafted orcrosslinked to the core.

Then, in the present application, the “core-shell rubber in the form ofprimary particles” may mean each unit body having the core-shellstructure, and the “core-shell rubber in the form of secondaryparticles” may mean an aggregate (or conglomerate) formed by clumpingtwo or more core-shell rubbers (particles) in the form of primaryparticles together. The core-shell rubbers may be dispersed and presentin the adhesive composition.

In one example, the core-shell rubber particles in the primary form andthe core-shell rubber particles in the secondary form can be preparedaccording to the methods described in the following examples. In thiscase, the aggregated rubbers in the secondary form produced by apolymerization reaction can be separated into smaller aggregated rubbersthrough a kneader such as a planetary mixer. In one example, all of theaggregated particles may not be separated in the form of completeprimary particles, and some of the secondary particles may be separatedinto primary particles and present in a mixed form of primary andsecondary particles. For example, the weight ratio of the primaryparticles may be 50 wt % or less, 40 wt % or less, 30 wt % or less, 20wt % or less, 10 wt % or less, 5 wt % or less, 4 wt % or less, 3 wt % orless, 2 wt % or less, 1 wt % or less, or 0.5 wt % or less, relative tothe total content of the core-shell rubbers. In one example, the weightratio of the primary particles may be substantially 0 wt %.Alternatively, the weight ratio of the primary particles may be, forexample, 0.01 wt % or more, 0.1 wt % or more, or 1 wt % or more.

In another example, the core-shell rubber particles in the primary formand the core-shell rubber particles in the secondary form may beprepared through a separate process.

The core may comprise a polymer of a diene-based monomer, or maycomprise a copolymer of a diene-based monomer and a heterogeneousmonomer component (not diene-based). Although not particularly limited,for example, butadiene or isoprene may be used as the diene-basedmonomer.

In one example, the core may be a butadiene-based core. For example, thecore may comprise a polymer of butadiene. In addition, the core maycomprise a copolymer of butadiene and another ethylenically unsaturatedmonomer. The ethylenically unsaturated monomer used upon core formationcan be exemplified by a vinyl-based aromatic monomer,(methyl)acrylonitrile, an alkyl (meth)acrylate, and the like, but is notparticularly limited thereto.

In one example, when the alkyl (meth)acrylate is additionally used incore formation, a different kind of alkyl (meth)acrylate from an alkyl(meth)acrylate used for shell formation, which is described below, canbe used in the core.

The shell grafted or crosslinked to the core may comprise an alkyl(meth)acrylate unit. The fact that the shell comprises an alkyl(meth)acrylate unit means that an alkyl (meth)acrylate monomer can beused upon forming a shell polymer that is crosslinked or grafted to thecore. In one example, as the alkyl (meth)acrylate, a lower alkyl(meth)acrylate having an alkyl group having 1 to 6 carbon atoms, such asmethyl methacrylate, ethyl methacrylate or t-butyl methacrylate can beused, without being limited to the above-listed monomers.

The shell may further comprise a vinylidene-based monomer unit. Forexample, it may further comprise a unit of an aromatic vinyl monomersuch as styrene, vinyl acetate or vinyl chloride. Although notparticularly limited, in one example, the shell may comprise an alkyl(meth)acrylate unit and an aromatic vinyl monomer unit.

In one example, the core and shell may have a predetermined glasstransition temperature (Tg). For example, the glass transitiontemperature (Tg) lower limit of the core may be −60° C. or more, −50° C.or more, or −40° C. or more. Although not particularly limited, theglass transition temperature upper limit of the core may be −20° C. orless, −25° C. or less, −30° C. or less, or −35° C. or less. In addition,the shell may have, for example, a glass transition temperature (Tg) of50° C. or more, 60° C. or more, or 70° C. or more. Although notparticularly limited, the glass transition temperature upper limit ofthe shell may be 120° C. or less. The glass transition temperature canbe measured according to a known method, and for example, can bemeasured using differential scanning calorimetry (DSC).

In one example, the core-shell rubber in the form of primary particlesmay have a ratio of the core particle diameter to the total core-shellparticle diameter (=thickness ratio of the core in the core-shell, R) of0.80 or more.

In the present application, the “particle diameter” may be used to meana diameter of a particle-shaped (for example, spherical or ellipsoidal)core-shell rubber or the configuration thereof, and may mean the lengthof the longest dimension when the shape of the core-shell rubber is notcompletely spherical or ellipsoidal. The particle diameter-relatedfeatures may be measured using known equipment, and for example, dynamiclighting scattering or laser diffraction equipment and the like may beused to identify the particle diameter-related features. Unlessspecifically defined, the particle diameter of the particles or particlesize of the particles may be used in the sense of the average particlediameter to be described below.

For example, the ratio of the core particle diameter to the totalcore-shell particle diameter may be 0.81 or more, 0.82 or more, 0.83 ormore, 0.84 or more, 0.85 or more, 0.86 or more, 0.87 or more, 0.88 ormore, 0.89 or more, or 0.90 or more. The upper limit of the ratio maybe, for example, 0.99, and specifically, may be 0.98 or less, 0.97 orless, 0.96 or less, 0.95 or less, 0.94 or less, 0.93 or less, or 0.92 orless. In the case of commercialized core-shell products, they do notsatisfy the above range in many cases, so that the impact absorptionfunction by the rubber is not sufficient, but the core-shell rubbersatisfying the above range can sufficiently absorb the impact applied tothe structure. In particular, when the ratio of the core exceeds 0.99,it becomes difficult for the shell to surround the core part while thethickness of the shell becomes thin, whereby a decrease in compatibilitywith the epoxy resin or a decrease in dispersibility may occur. Inaddition, when the ratio of the core is less than 0.8, the effect ofimproving the impact strength is insufficient.

For example, when the core-shell rubber in the form of primary particleshas an average particle diameter of 250 nm or more, 260 nm or more, 270nm or more, 280 nm or more, 290 nm or more, or 300 nm or more, and forexample, the upper limit thereof is 600 nm or less or 500 nm or less,specifically, 450 nm or less, 440 nm or less, 430 nm or less, 420 nm orless, 410 nm or less, or 400 nm or less, the core-shell rubber in theform of primary particles may have a size that can satisfy the aboveratio (R). At this time, the ‘average particle diameter” means thediameter that the particle with 50% of the cumulative weight (mass) inthe particle size distribution curve has (passes). For example, the coreof the core-shell rubber in the form of primary particles may have anaverage particle diameter of 180 nm or more, 200 nm or more, 220 nm ormore, 240 nm or more, 260 nm or more, 280 nm or more, 300 nm or more,and the upper limit thereof may be, for example, 500 nm or less, 495 nmor less, 490 nm or less, specifically, 450 nm or less, 400 nm or 350 nmor less. In the case of commercialized core-shell products, the size andratio (R) of the corresponding particle diameter do not satisfy theabove range in many cases, so that the impact absorption function by therubber is not sufficient.

In another example, the core-shell rubber in the form of primaryparticles may have an average particle diameter of 250 nm or less. Inthis case, the lower limit thereof may be, for example, 10 nm or more,20 nm or more, or 30 nm or more. Even in the case of having such aparticle diameter, the core-shell rubber in the form of primaryparticles may have the ratio (R) of the core particle diameter to thetotal core-shell particle diameter satisfying the above range. In thecase of commercialized core-shell products, the size of thecorresponding particle diameter does not satisfy the above range in manycases, so that the impact absorption function by the rubber is notsufficient.

Also, in the present application, the core-shell rubber may have apredetermined particle size distribution.

In one example, the core-shell rubber in the form of primary particlesmay have a diameter of D₁₀ in the particle diameter distribution, thatis, a diameter up to cumulative 10% particles on the basis of weight(mass), from the smaller side of the particle diameters by the particlesize distribution measurement, in a range of 180 to 220 nm.

In another example, the core-shell rubber in the form of primaryparticles may have a diameter of D₅₀ in the particle diameterdistribution, that is, a diameter up to cumulative 50% particles on thebasis of weight (mass), from the smaller side of the particle diametersby the particle size distribution measurement, in a range of 250 to 350nm.

In another example, the core-shell rubber in the form of primaryparticles may have a diameter of D₉₀ in the particle diameterdistribution, that is, a diameter up to cumulative 90% particles on thebasis of weight (mass), from the smaller side of the particle diametersby the particle size distribution measurement, in a range of 450 to 510nm.

In one example, the core-shell rubber in the form of primary particlesmay have a particle size distribution width of 2.0 or less or 1.5 orless obtained by the following equation 1. The lower limit thereof isnot particularly limited, which may be, for example, 0.5 or more, 0.6 ormore, 0.7 or more, 0.8 or more, 0.9 or more, or 1.0 or more.

(D₉₀−D₁₀)/(D₅₀)  [Equation 1]

As described above, when the core-shell rubber having a narrow particlesize distribution width is used, it is advantageous to uniformly secureexcellent adhesion strength, peel strength, and impact-resistantstrength in a wide temperature range.

Such particle diameter characteristics can be obtained through, forexample, a method of appropriately adjusting the type or content ofmonomers used upon core or shell formation, or a method of dividing themonomers into several stages to be introduced or appropriately adjustingthe polymerization time of the core or shell or other polymerizationconditions, and the like.

In one example, the number of primary particles aggregated for secondaryparticle formation is not particularly limited. For example, the primaryparticles may be aggregated to form secondary particles, so that thecore-shell rubber conglomerate (aggregate), that is, the secondaryparticles may have a diameter in a range of 0.1 to 10 In one example,the core-shell rubber (aggregated particles) in the form of secondaryparticles, which has undergone a kneading process through a kneader suchas a planetary mixer after polymerization, may have a size of 2 μm orless, 1.5 μm or less, 1 μm or less, or 0.5 μm or less. In relation tothe secondary particles, the size may be used in the sense correspondingto the particle diameter or the size of the longest dimension asdescribed above.

In one example, the average particle diameter of the core-shell rubberin the form of secondary particles may be 1.5 μm or less, or 1 μm orless. Specifically, the average particle diameter of the core-shellrubber may be 900 nm or less, 800 nm or less, 700 nm or less, or 600 nmor less. Although not particularly limited, the average particlediameter lower limit of the core-shell rubber in the form of secondaryparticles may be 100 nm or more, 200 nm or more, 300 nm or more, 400 nmor more, or 500 nm or more.

The core-shell rubber in the form of secondary particles satisfying theabove-described characteristics may be included in an amount of 5 partsby weight or more based on the total content of the adhesivecomposition. Specifically, the lower limit of the content may be 6 partsby weight or more, 7 parts by weight or more, 8 parts by weight or more,9 parts by weight or more, or 10 parts by weight or more. In addition,the content of the core-shell rubber conglomerate may be 35 parts byweight or less. Specifically, the upper limit of the content may be 34parts by weight or less, 33 parts by weight or less, 32 parts by weightor less, 31 parts by weight or less, or 30 parts by weight or less, andmore specifically, may be 25 parts by weight or less, or 20 parts byweight or less. When it is used less than the content, the impactstrength improvement effect is not sufficient, and when it is used inexcess of the above range, it is not preferable because shear strengthand high-temperature impact strength may be lowered.

In one example, the adhesive composition may further comprise a liquidrubber.

In one example, the liquid rubber may be a configuration having an epoxygroup at the end of the liquid rubber, which is a homopolymer of adiene-based monomer or a copolymer of a diene-based monomer and aheterogeneous monomer. That is, the liquid rubber may be an epoxyterminated liquid rubber.

For example, the liquid rubber may comprise a homopolymer or copolymerhaving repeating units derived from butadiene or isobutadiene. In theliquid rubber, for example, a copolymer of butadiene or isobutadiene andan acrylate and/or an acrylonitrile may be included.

In one example, the content of the liquid rubber may be the same as thatof the above-described core-shell rubber.

In one example, the adhesive composition may comprise at least 5 partsby weight or 10 parts by weight or more of a rubber (core-shell rubberand/or liquid rubber) based on the total content of the adhesivecomposition. For example, when the adhesive composition comprises onlythe core-shell rubber, the adhesive composition may comprise at least 5parts by weight or 10 parts by weight or more of the core-shell rubberbased on the total content of the adhesive composition. Alternatively,when the adhesive composition comprises both the core-shell rubber andthe liquid rubber, the adhesive composition may comprise at least 5parts by weight or 10 parts by weight or more of the core-shell rubberand the liquid rubber based on the total content of the adhesivecomposition. Even in such a case, the rubber components may be used inan amount of 35 parts by weight or less, in consideration of shearstrength and high-temperature impact strength. In one example, theadhesive composition may comprise a rubber (core-shell rubber and/orliquid rubber) in an amount of 10 parts by weight or more, 12 parts byweight or more, or 14 parts by weight or more, and 30 parts by weight orless, 25 parts by weight or less, or 22 parts by weight or less, basedon the total content of the adhesive composition.

(d) Epoxy Curing Agent

The adhesive composition may comprise a predetermined curing agent sothat it can be cured at a temperature of about 80° C. or more, or about100° C. or more. If the curing can occur in the above temperature range,the type of the curing agent is not particularly limited. For example,as the curing agent, a dicyandiamide, a melamine, a diallyl melamine, aguanamine (e.g. acetoguanamine, benzoguanamine), an aminotriazole(3-amino-1,2,4-triazole), a hydrazide (adipic acid dihydride, stearicacid dihydrazide, isophthalic acid dihydrazide), a cyanoacetamide or anaromatic polyamine (e.g.: diaminodiphenylsulfone), and the like can beused.

Although not particularly limited, the curing agent may be used in anamount of, for example, 1 part by weight or more, 2 parts by weight ormore, 3 parts by weight or more, or 4 parts by weight or more, based onthe total content of the adhesive composition. Although not particularlylimited, the content upper limit of the curing agent may be 15 parts byweight or less, 14 parts by weight or less, 13 parts by weight or less,12 parts by weight or less, 11 parts by weight or less, or 10 parts byweight or less.

(e) Additional Components

In one example, the adhesive composition may further comprise a urethaneresin. The urethane resin may be a urethane resin in which isocyanateends are blocked.

(e-1) In one example, the urethane resin may be a urethane resin havinga polyether structure. In addition, at least one of the isocyanategroups which are terminals of the urethane resin has a structure(capping structure) terminated with a predetermined compound.

The urethane resin may contain an isocyanate unit and a polyether polyolunit. In the present application, the fact that the urethane resincontains a predetermined unit may mean a state where in a resinstructure (main chain or side chain) formed by reacting one or morecompounds, the unit derived as the compounds are polymerized is includedtherein.

The specific kind of isocyanate used in the urethane resin is notparticularly limited, and a known aromatic or non-aromatic isocyanatemay be used. In a non-limiting example, the isocyanate can benonaromatic. That is, upon forming the modified urethane resin, anisocyanate of aliphatic or alicyclic series may be used. In the case ofusing the non-aromatic isocyanate, impact resistance, or viscositycharacteristics of the adhesive composition may be improved.

The kind of the usable non-aromatic isocyanate is not particularlylimited. For example, an aliphatic polyisocyanate or its modifiedproducts can be used. Specifically, an aliphatic polyisocyanate such ashexamethylene diisocyanate, trimethylhexamethylene diisocyanate, lysinediisocyanate, norbornane diisocyanate methyl, ethylene diisocyanate,propylene diisocyanate or tetramethylene diisocyanate; an alicyclicpolyisocyanate such as transcyclohexane-1,4-diisocyanate, isophoronediisocyanate, bis(isocyanatemethyl) cyclohexane diisocyanate ordicyclohexylmethane diisocyanate; or a carbodiimide-modifiedpolyisocyanate or isocyanurate-modified polyisocyanate of at least oneof the foregoing; and the like can be used. In addition, a mixture oftwo or more of the above-listed compounds can be used.

In one example, the polyol may be a polyol having an OH equivalent of300 or more. For example, the OH equivalent lower limit of the polyolmay be 400 or more, 500 or more, 600 or more, 700 or more, 800 or more,or 900 or more. The OH equivalent upper limit of the polyol is notparticularly limited, but may be, for example, 2,000 or less, 1,900 orless, 1,800 or less, 1,700 or less, 1,600 or less, 1,500 or less, 1,400or less, 1,300 or less, 1,200 or less, or 1,100 or less. When theequivalent range is satisfied, it is advantageous to improveimpact-resistant characteristics, adhesion strength characteristics andpeeling characteristics of the adhesive.

The kind of the polyol is not particularly limited as long as theequivalent is satisfied. For example, a tetrafunctional polyol such aspentaerythritol; a trifunctional polyol such as glycerin ortrimethylolpropane; or a bifunctional polyol such as glycol may be used.In one example, a polyalkylene glycol may be used as the polyol, withoutbeing particularly limited thereto. Specifically, for example,polypropylene glycol may be used as the polyalkylene glycol.

In one example, the urethane resin may comprise a branched polyetherpolyol unit, and a non-aromatic isocyanate unit.

In one example, the polyol may be branched polypropylene glycol. Thebranched polypropylene means that the polypropylene backbone isconfigured to have side chains, which may be distinguished from thelinear shape, that is, the case where the polypropylene repeating unitdoes not have side chains. For example, the branched polypropylene hasbranches in which a-olefins, such as ethylene, 1-butene, 1-hexene or4-methyl-1-pentene, are incorporated (copolymerized) into thepolypropylene backbone. That is, in one example of the presentapplication, the polyol may have a branched polypropylene unit. When thebranched polypropylene glycol is used, it is advantageous for strengthimprovement.

As mentioned above, the urethane resin may have a structure in which oneor more of its isocyanate ends are terminated by a predeterminedcompound. The so-called capping method of the isocyanate end in theurethane resin is not particularly limited. Known techniques can beused. For example, a polymer or prepolymer, which is derived from anether-based polyol, having urethane groups in urethane chains and havingisocyanate groups at their ends is prepared, where the isocyanate endsof the urethane can be capped through a compound having an activehydrogen group at all or part of the isocyanate groups. In anotherexample, upon preparing the urethane resin, a method of cappingsimultaneously with polymerization by introducing a compound capable ofcapping the isocyanate ends together may be used. The kind of thecompound which is capable of capping isocyanate ends is not specificallylimited, and for example, an amine-based compound, a phenol-basedcompound, an oxime-based compound, or a bisphenol-based compound can beused.

In one example, the urethane resin may have a weight average molecularweight (Mw) of 3,000 to 40,000. The weight average molecular weight maybe a polystyrene conversion molecular weight measured by GPC. Morespecifically, the lower limit of the weight average molecular weight ofthe urethane resin may be 3,000 or more, 3,500 or more, 4,000 or more,4,500 or more, 5,000 or more, 5,500 or more, 6,000 or more, 6,500 ormore, 7,000 or more, 7,500 or more, 8,000 or more 8,500 or more, or9,000 or more. Although not particularly limited, the upper limit of theweight average molecular weight of the urethane resin may be 35,000 orless, or 30,000 or less. When the above range is satisfied, it ispossible to provide advantageous physical properties to the adhesive.The urethane resin may have a molecular weight controlled using abranching agent, a chain extender or the like upon its manufacture, andmay also have a linear structure or a branched structure. In the case ofthe branched structure, it is appropriate to polymerize the urethanewithout using a chain extender, which is advantageous for obtaining anappropriate molecular weight. When polypropylene glycol is used as thepolyol, the degree of contribution to improving the impact strength ofthe urethane resin having a branched structure may be higher.

In one example, the adhesive composition may comprise 5 parts by weightor more of the modified urethane resin based on the content of theentire adhesive composition. Specifically, the content of the modifiedurethane resin may be 6 parts by weight or more, 7 parts by weight ormore, 8 parts by weight or more, 9 parts by weight or more, or 10 partsby weight or more. Although not particularly limited, the content upperlimit of the urethane resin may be, for example, 25 parts by weight orless. More specifically, the urethane resin may be used in an amount of20 parts by weight or less, 19 parts by weight or less, 18 parts byweight or less, 17 parts by weight or less, 16 parts by weight or less,or 15 parts by weight or less. When the urethane resin is used in anamount of less than the above range, the impact strength improvement isnot sufficient, and when it is used in an amount of more than the aboverange, there is a problem that shear strength is lowered andhigh-temperature impact strength is lowered.

(e-2) In another example, the urethane resin is a modified urethaneresin having a unit derived from polytetrahydrofuran, where at least oneof the isocyanate groups which are terminals of the urethane resin mayhave a structure (capping structure) terminated with a predeterminedcompound, as described below.

The urethane resin may comprise an isocyanate unit, a polyol unit, apolytetrahydrofuran unit. In the present application, the fact that theurethane resin comprises predetermined units may mean a state where in aresin structure (main chain or side chain) formed by reaction of one ormore compounds, the compounds are polymerized and simultaneously theunits derived therefrom are included in the resin structure.

The specific kind of isocyanate used in the urethane resin is notparticularly limited, and a known aromatic or non-aromatic isocyanatemay be used. In a non-limiting example, the isocyanate can benonaromatic. That is, upon forming the modified urethane resin, anisocyanate of aliphatic or alicyclic series may be used. In the case ofusing the non-aromatic isocyanate, impact resistance, or viscositycharacteristics of the adhesive composition may be improved.

The kind of the usable non-aromatic isocyanate is not particularlylimited. For example, an aliphatic polyisocyanate or its modifiedproducts can be used. Specifically, an aliphatic polyisocyanate such ashexamethylene diisocyanate, trimethylhexamethylene diisocyanate, lysinediisocyanate, norbornane diisocyanate methyl, ethylene diisocyanate,propylene diisocyanate or tetramethylene diisocyanate; an alicyclicpolyisocyanate such as transcyclohexane-1,4-diisocyanate, isophoronediisocyanate, bis(isocyanatemethyl) cyclohexane diisocyanate ordicyclohexylmethane diisocyanate; or a carbodiimide-modifiedpolyisocyanate or isocyanurate-modified polyisocyanate of at least oneof the foregoing; and the like can be used. In addition, a mixture oftwo or more of the above-listed compounds can be used.

The kind of the polyol used at the time of forming the urethane resin isnot particularly limited. For example, a tetrafunctional polyol such aspentaerythritol; a trifunctional polyol such as glycerin ortrimethylolpropane; or a bifunctional polyol such as glycol may be used.In one example, a polyalkylene glycols such as polypropylene glycol maybe used as the glycol.

In one example, a linear polyol may be used as the polyol. For example,a linear shape such as polypropylene glycol can be used. The linearpolyol is a polyol having two hydroxyl groups in the molecule, which mayusually mean one having hydroxyl groups at both ends of the molecule.Conversely, the polyol having three or more hydroxyl groups in themolecule can be said to be a branched polyol. Compared with the case ofusing a branched shape, the case of using a linear polyol makes it easyto control the molecular weight of the urethane resin in the rangedescribed below, which may be advantageous for improving theimpact-resistant characteristics of the adhesive.

In one example, the polyol may be a polyol having an OH equivalent of300 or more. For example, the OH equivalent lower limit of the polyolmay be 400 or more, 500 or more, 600 or more, 700 or more, 800 or more,or 900 or more. The OH equivalent upper limit of the polyol is notparticularly limited, but may be, for example, 2,000 or less, 1,900 orless, 1,800 or less, 1,700 or less, 1,600 or less, 1,500 or less, 1,400or less, 1,300 or less, 1,200 or less, or 1,100 or less. When theequivalent range is satisfied, it is advantageous to improveimpact-resistant characteristics, adhesion strength characteristics andpeeling characteristics of the adhesive.

As described above, the urethane resin may have a structure in which oneor more of its isocyanate ends are terminated by a predeterminedcompound. The so-called capping method of the isocyanate end in theurethane resin is not particularly limited. Known techniques can beused. For example, upon preparing the modified urethane resin, a methodof introducing a compound capable of capping the isocyanate endstogether thereto and polymerizing it may be used. The kind of thecompound which is capable of capping isocyanate ends is not specificallylimited, and for example, an amine-based compound, a phenol-basedcompound, an oxime-based compound, or a bisphenol-based compound can beused.

In one example, the urethane resin may comprise a unit in which theisocyanate end is terminated by polytetrahydrofuran. Since polytetrahydrofuran also has OH groups, the urethane resin may further comprise aunit in which the isocyanate end terminated by polytetrahydrofuran, whenthe urethane resin of the present application is synthesized byso-called one-pot synthesis.

In one example, the polytetrahydrofuran may have a weight averagemolecular weight (Mw) of 500 or more. In the present application, the“weight average molecular weight (Mw)” may be a polystyrene conversionmolecular weight measured by GPC. For example, the weight averagemolecular weight of the polytetrahydrofuran may be 550 or more, 600 ormore, 650 or more, 700 or more, 750 or more, 800 or more, or 850 ormore. In one example, the weight average molecular weight upper limit ofthe polytetrahydrofuran may be 4,000 or less. Specifically, the weightaverage molecular weight of the polytetrahydrofuran may be 3,000 orless, or 2,000 or less, and may be, more specifically, 1,500 or less,1,400 or less, 1,300 or less, or 1,200 or less.

In one example, the polytetrahydrofuran may have an OH equivalent of 400to 2,200. When the OH equivalent is out of the above range, theimpact-resistant characteristics of the adhesive may be lowered.Considering the impact-resistant characteristics, the polytetrahydrofuran may have, for example, an OH equivalent of 450 or more, or500 or more, and may have an OH equivalent of 1,100 or less, or 1,000 orless.

In one example, the weight average molecular weight of the urethaneresin having the above configuration may be in the range of 5,000 to30,000. When the above range is satisfied, the physical propertiessuitable for the adhesive application of the present application can beprovided.

In one example, the adhesive composition may comprise 5 parts by weightor more of the modified urethane resin based on the content of theentire adhesive composition. Specifically, the content of the modifiedurethane resin may be 6 parts by weight or more, 7 parts by weight ormore, 8 parts by weight or more, 9 parts by weight or more, or 10 partsby weight or more. Although not particularly limited, the content upperlimit of the urethane resin may be, for example, 25 parts by weight orless. More specifically, the urethane resin may be used in an amount of20 parts by weight or less, 19 parts by weight or less, 18 parts byweight or less, 17 parts by weight or less, 16 parts by weight or less,or 15 parts by weight or less. When the urethane resin is used in anamount of less than the above range, the impact strength improvement isnot sufficient, and when it is used in an amount of more than the aboverange, there is a problem that shear strength is lowered andhigh-temperature impact strength is lowered.

If) Other Components

The adhesive composition may comprise a catalyst to control the rate andtemperature of the curing reaction by the curing agent. The type of thecatalyst is not particularly limited, and various kinds of knowncatalysts may be appropriately used.

In one non-limiting example, as the catalyst, urea series such asp-chlorophenyl-N,N-dimethylurea, 3-phenyl-1,1-dimethylurea or3,4-dichlorophenyl-N,N-dimethylurea; tertiary acrylics; amines such asbenzyldimethylamine; piperidine or derivatives thereof; or imidazolederivatives may be used.

Although not particularly limited, the catalyst may be used, forexample, in an amount of 0.1 parts by weight or more, 0.2 parts byweight or more, 0.3 parts by weight or more, or 0.4 parts by weight ormore, based on the total content of the adhesive composition. Althoughnot particularly limited, the upper limit of the catalyst content may be2 parts by weight or less.

In one example, the adhesive composition may further comprise aparticulate inorganic filler, that is, inorganic particles. When theinorganic filler is used, it is possible to adjust the mechanicalproperties, rheological properties and the like of the adhesive. Theform of the inorganic filler may be rectangular, spherical, platy oracicular, which is not particularly limited.

As the inorganic filler, for example, calcium oxide, quartz powder,alumina, calcium carbonate, calcium oxide, aluminum hydroxide, magnesiumcalcium carbonate, barite, hydrophilic or hydrophobic silica particles,or aluminum magnesium calcium silicate can be used. When silicaparticles are used, it is more preferable that they have hydrophobicity.

Although not particularly limited, the inorganic filler may be used inan amount of, for example, 1 part by weight or more, 2 parts by weightor more, 3 parts by weight or more, or 4 parts by weight or more, basedon the total content of the adhesive composition. Although notparticularly limited, the upper limit of the inorganic filler contentmay be 15 parts by weight or less, or 10 parts by weight or less.

In one example, the composition may further comprise various kinds ofadditives. For example, known plasticizers, reactive or non-reactivediluents, coupling agents, fluidity modifiers, thixotropic agents,colorants, and the like may further be included in the adhesivecomposition. The specific kind of the additive is not particularlylimited, and known materials or commercial products may be used withoutlimitation.

Although not particularly limited, the additive may be used in an amountof, for example, 0.1 parts by weight or more, 1 part by weight or more,2 parts by weight or more, or 3 parts by weight or more, based on thetotal content of the adhesive composition. Although not particularlylimited, the upper limit of the additive content may be 15 parts byweight or less, 14 parts by weight or less, 13 parts by weight or less,12 parts by weight or less, 11 parts by weight or less, or 10 parts byweight or less.

In another example of the present application, the present applicationrelates to a structure comprising a cured product of the adhesivecomposition. The structure may comprise a base material and a curedproduct of the adhesive composition cured after being applied on thebase material. The base material may comprise a metal component, aplastic component, wood, a glass fiber-containing base material, and thelike.

In one example, the structure may have a form in which two or more basematerials are bonded via the cured product. For example, the structuremay have a form in which a metal and a metal are bonded via the curedproduct, a form in which a metal and a plastic are bonded via the curedproduct, or a form in which a plastic and a plastic are bonded via thecured product. The structure can be used as a structural material foraerospace, wind power generation, ships or automobiles.

In another example of the present application, the present applicationrelates to a method for producing a structure. The method may comprisesteps of applying a composition having a configuration as describedabove on a surface of a base material and curing the composition appliedto the surface of the base material. The application may be performedsuch that physical contact between the base material and the adhesivecomposition occurs.

The method of applying the adhesive composition to the surface of thestructure is not particularly limited. For example, jet spraying methodssuch as swirl or streaming, or mechanical application by an extrusionmethod can be used. The application may be made to one or more basematerials to be bonded.

The curing temperature is not particularly limited. For example, thecuring may be performed at 80° C. or more, or 100° C. or more. Althoughnot particularly limited, considering heat-resistant stability, it ispreferable to perform the curing at a temperature of 220° C. or less.

Advantageous Effects

According to one example of the present application, an adhesivecomposition providing excellent adhesion strength, peel strength andimpact-resistant strength uniformly over a wide temperature range can beprovided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the particle size distribution of the core-shell rubbers(in the form of primary particles) prepared according to one embodimentof the present application. The horizontal axis means particlediameters, and the vertical axis means relative numbers of rubbers.

FIG. 2 is an image taken to the appearance that the core-shell rubbersprepared according to one embodiment of the present application aredispersed in an epoxy resin.

BEST MODE

Hereinafter, the present application will be described through examplesand comparative examples. However, the scope of the present applicationis not limited by the scope set forth below.

Production Examples

* Production Example 1: Production of Core-Shell Rubber Assembly

First step (production of core): 70 parts by weight of ion-exchangedwater, 60 parts by weight of 1,3-butadiene as a monomer, 1.0 part byweight of sodium dodecylbenzene sulfonate as an emulsifier, 0.85 partsby weight of calcium carbonate, 0.28 parts by weight of tertiary dodecylmercaptan and 0.28 parts by weight of persulfate potassium as aninitiator were introduced into a nitrogen-substituted polymerizationreactor, and reacted at 75° C. until a polymerization conversion ratiowas 30 to 40%. Thereafter, 0.3 parts by weight of sodium dodecylbenzenesulfonate was introduced thereto, 20 parts by weight of 1.3-butadienewas further introduced thereto, and the temperature was raised to 80° C.to terminate the reaction at the time when the polymerization conversionratio was 95%. The produced polymer had a latex gel content of 73%. Atthis time, the rubber latex was coagulated with a dilute acid or a metalsalt, and then washed, dried in a vacuum oven at 60° C. for 24 hours,and 1 g of the resulting rubber was placed in 100 g of toluene andstored in a dark room at room temperature for 48 hours, and then thelatex gel content was measured by separating the sol and the gel.

Second step: 70 parts by weight of the produced rubber latex was putinto a closed reactor, and the temperature of the reactor filled withnitrogen was raised to 75° C. Thereafter, 0.1 parts by weight of sodiumpyrophosphate, 0.2 parts by weight of dextrose and 0.002 parts by weightof ferrous sulfide were introduced into the reactor in a lump.

In a separate mixing device, 25.5 parts by weight of methylmethacrylate, 4.5 parts by weight of styrene, 0.5 parts by weight ofsodium dodecylbenzene sulfonate as an emulsifier, 0.1 parts by weight ofcumene hydroperoxide and 20 parts by weight of ion-exchanged water weremixed to prepare a monomer emulsion.

To the reactor to which the rubber latex had been introduced, theemulsion was continuously added over 3 hours, and then, after 30minutes, 0.03 parts by weight of hydroperoxide was added and aged at thesame temperature for 1 hour to terminate the reaction at the time whenthe polymerization conversion ratio was 98%.

At an appropriate time in the process, the average particle diameter ofthe core measured by Nicomp N300 dynamic light scattering equipment was320 nm, and the average particle diameter of the core-shell rubber resinlatex was 345 nm.

In addition, the particle size distribution of the produced core-shellrubber in the form of primary particles was measured, and the resultswere described in FIG. 1.

Thereafter, an antioxidant was added to the reactant, aggregated withmagnesium sulfate, and then dehydrated and dried to produce a core-shellrubber in an aggregated form.

* Production Example 2: Production of Modified Epoxy Resin

80 g of amine-terminated polypropylene glycol having an amine equivalentof 1,000 and 100 g of a bisphenol A epoxy resin having an epoxyequivalent of 190 were mixed in a nitrogen-substituted polymerizationreactor, and the reaction was performed at 75° C. for 3 hours to producean ether-containing modified epoxy resin.

* Production Example 3: Production of Modified Epoxy Resin

30 g of amine-terminated polypropylene glycol having an amine equivalentof 200 and 100 g of a bisphenol A epoxy resin having an epoxy equivalentof 190 were mixed in a nitrogen-substituted polymerization reactor, andthe reaction was performed at 75° C. for 3 hours to produce anether-containing modified epoxy resin.

* Production Example 4: Production of Structural Adhesive

The compositions of Examples and Comparative Examples containing thecomponents shown in Table 1 below in predetermined contents (weightratio:parts by weight) were prepared as adhesive materials.Specifically, the core-shell rubber conglomerates and the epoxy resinswere placed in a planetary mixer and mixed at 80° C. for 5 hours. Theappearance that the core-shell rubbers are dispersed in the epoxy resinis as shown in FIG. 2. Thereafter, the remaining components excluding‘the urethane resin, the curing agent and the catalyst’ were placed inthe planetary mixer and stirred at 80° C. for 3 hours. Finally, thetemperature was lowered to 40° C., ‘the urethane resin, the curing agentand the catalyst’ were put in the planetary mixer and mixed for 1 hour,and then the temperature was lowered to room temperature (about 23° C.)to terminate the kneading.

Method of Measuring Physical Properties

* Impact Peel Strength

Five specimens were manufactured for each of Examples and ComparativeExamples, and an object weighing 45 kg was dropped freely at a rate of 2m/s at a height of 1.5 m in accordance with DIN ISO 11343, and theimpact peel strength (unit: N/mm) was measured at each of 80° C., 23° C.and −40° C. and the average value was taken.

In the case of the specimen, two cold rolled steel having a size of 90mm×25 mm×1.6 mm (length×width×thickness) and a strength of 440 MPa wereprepared, and the adhesive was applied to a predetermined area of thecold rolled steel so that the adhesive area of the cold rolled steel was25 mm×30 mm, and cured at 180° C. for 20 minutes. Using glass beads, thethickness of the adhesive layer was kept uniform at 0.2 mm. Themeasurement results were described in Table 2.

* Shear Strength Experiment

For the specimens prepared in connection with Examples and ComparativeExamples, five shear strength measurements were performed in accordancewith DIN EN 1465 and the average value was taken. At this time, theshear strength (unit: Mpa) measurement was made under conditions of 10mm/min and 23° C.

In the case of the specimen, two cold rolled steel sheets having a sizeof 100 mm×25 mm×1.6 mm (length×width×thickness) and a strength of 440MPa were prepared, and the adhesive was applied to a predetermined areaof the cold rolled steel so that the adhesive area of the cold rolledsteel was 25 mm×10 mm, and cured at 180° C. for 20 minutes. Using glassbeads, the thickness of the adhesive layer was kept uniform at 0.2 mm.The measurement results were described in Table 2.

Experiment results

TABLE 1 Example Comparative Example 1 2 1 2 3 4 First epoxy resin¹⁾ 3434 54 34 29 34 Second epoxy resin²⁾ 5 − 5 5 5 5 Modified epoxy resin³⁾20 15 − 20 − − Modified epoxy resin⁴⁾ − 5 − − − 20 Core-shell rubber⁵⁾15 15 15 − − 15 Core-shell rubber⁶⁾ − 5 − 15 − − Liquid rubber⁶⁾ − − − −40 − Urethane resin⁸⁾ 5 5 5 5 5 5 Diluent (mono 1.6 1.6 1.6 1.6 1.6 1.6epoxy resin)⁹⁾ Colorant¹⁰⁾ 0.05 0.05 0.05 0.05 0.05 0.05 Curing agent¹¹⁾5 5 5 5 5 5 Catalyst¹²⁾ 1 1 1 1 1 1 CaCO₃ 7 7 7 7 7 7 Wollastonite 3 3 33 3 3 Fumed silica¹³⁾ 3 3 3 3 3 3 Silane coupling agent¹⁴⁾ 0.35 0.350.35 0.35 0.35 0.35 Total 100 100 100 100 100 100 1. First epoxyresin¹⁾: Bisphenol A-based epoxy resin (YD128) having an epoxyequivalent of less than 300 2. Second epoxy resin²⁾: Bisphenol A-basedepoxy resin (YD011) having an epoxy equivalent of 300 or more 3.Modified epoxy resin³⁾: Resin prepared in Production Example 2 4.Modified epoxy resin⁴⁾: Resin prepared in Production Example 3 5.Core-shell rubber⁵⁾: Core-shell rubber of Production Example 1 6.Core-shell rubber⁶⁾: Pralloid EXL 2600 from DOW 7. Liquid rubber⁶⁾:Struktol polydis 3604 8. Urethane resin⁸⁾: QR-9466 from Adeka 9. Diluent(mono epoxy resin)⁹⁾: NC513 from Cardolite 10. Colorant¹⁰⁾: Pigmentviolet 23 11: Curing agent¹¹⁾: Airproduct 1200G 12: Catalyst¹²⁾: EvonikAmicure UR7/10 13: Fumed silica¹³⁾: Cabo TS720 14: Silane couplingagent¹⁴⁾: GE Advanced material A-187

TABLE 2 Example Comparative Example 1 2 1 2 3 4 Impact strength (−40°C.) 35 31  7 X  5  8 Impact strength (23° C.) 40 41 30 38 30 35 Impactstrength (80° C.) 43 38 27 36 25 30 Shear strength (23° C.) 37 38 28 3525 30 X: the case where the stably measured value is not obtainedbecause the measured value is very low

1. An adhesive composition comprising: (a) one or more epoxy resins; (b)a modified epoxy resin having a polyether structure, wherein themodified epoxy resin having the polyether structure is a reactant of anamine-terminated polyether and an epoxy resin; (c) a core-shell rubberin the form of secondary particles, wherein the secondary particlescomprise two or more core-shell rubbers in the form of primary particleswhich are aggregated; and (d) one or more epoxy curing agents.
 2. Theadhesive composition according to claim 1, wherein the modified epoxyresin (b) having the polyether structure comprises an amine-terminatedpolyalkylene glycol having an amine equivalent in a range of 300 to2,000 and the epoxy resin having an epoxy equivalent in a range of 150to
 300. 3. The adhesive composition according to claim 1, wherein theone or more epoxy resins (a) comprise a bisphenol A-based epoxy resinand a bisphenol F-based epoxy resin.
 4. The adhesive compositionaccording to claim 3, wherein the one or more epoxy resins (a) have atleast one epoxy resin having a first epoxy equivalent of less than 300and another epoxy resin having a second epoxy equivalent of 300 or more.5. The adhesive composition according to claim 1, wherein the adhesivecomposition comprises 35 parts by weight or less of the modified epoxyresin, based on a content of the entire adhesive composition.
 6. Theadhesive composition according to claim 1, wherein the two or morecore-shell rubbers in the form of primary particles have an averageparticle diameter of 250 nm to 500 nm.
 7. The adhesive compositionaccording to claim 1, wherein cores in the two or more core-shellrubbers in the form of primary particles have an average particlediameter of 180 to 495 nm.
 8. The adhesive composition according toclaim 5, wherein the two or more core-shell rubbers in the form ofprimary particles have a ratio of a core particle diameter to a totalparticle diameter of core-shell particles satisfying 0.8 to 0.99.
 9. Theadhesive composition according to claim 1, wherein the core-shell rubber(c) in the form of secondary particles has an average particle diameterof 2 μm or less.
 10. The adhesive composition according to claim 1,wherein the core-shell rubber has butadiene-based cores.
 11. Theadhesive composition according to claim 1, wherein the adhesivecomposition comprises 5 to 35 parts by weight of the core-shell rubber(c) in the form of secondary particles based on a total content of theadhesive composition.
 12. The adhesive composition according to claim 1,further comprising a urethane resin with a polyether structurecomprising a polyether polyol unit and a non-aromatic isocyanate unit,wherein the urethane resin has at least one of isocyanate endsterminated with an amine-based compound, a phenol-based compound, anoxime-based compound, or a bisphenol-based compound.
 13. The adhesivecomposition according to claim 12, wherein the polyether polyol unit hasan OH equivalent in a range of 300 to 2,000.
 14. A structure comprisinga cured product of the adhesive composition according to claim
 1. 15. Amethod for producing a structure comprising: contacting the adhesivecomposition according to claim 1 with a surface of a base material; andcuring the adhesive composition in contact with the surface of the basematerial.